linux-kernel - Re: [PATCH v7 2/9] dt-bindings: display/msm: dp-controller: fix fallback for SM6350

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Message-ID: <24999a53-ea5a-4823-a84f-2ca0ca184bb4@linaro.org>
Date: Tue, 2 Sep 2025 08:04:54 +0200
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Cc: Rob Clark <robin.clark@....qualcomm.com>,
 Dmitry Baryshkov <lumag@...nel.org>, Abhinav Kumar
 <abhinav.kumar@...ux.dev>, Jessica Zhang <jessica.zhang@....qualcomm.com>,
 Sean Paul <sean@...rly.run>, Marijn Suijten <marijn.suijten@...ainline.org>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Kuogee Hsieh <quic_khsieh@...cinc.com>,
 Abel Vesa <abel.vesa@...aro.org>, Mahadevan <quic_mahap@...cinc.com>,
 Bjorn Andersson <andersson@...nel.org>,
 Konrad Dybcio <konradybcio@...nel.org>, linux-arm-msm@...r.kernel.org,
 dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 2/9] dt-bindings: display/msm: dp-controller: fix
 fallback for SM6350

On 02/09/2025 06:03, Dmitry Baryshkov wrote:
> On Mon, Sep 01, 2025 at 05:45:49AM +0200, Krzysztof Kozlowski wrote:
>> On Fri, Aug 29, 2025 at 01:48:15AM +0300, Dmitry Baryshkov wrote:
>>> The SM6350 doesn't have MST support, as such it is not compatible with
>>> the SM8350 platform. Add new entry for SM6350 with fallback to SC7180
>>> (which belongs to the same generation and also doesn't have MST
>>> support).
>>>
>>> Fixes: 39086151593a ("dt-bindings: display: msm: dp-controller: document SM6350 compatible")
>>> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
>>> ---
>>>  .../devicetree/bindings/display/msm/dp-controller.yaml     | 14 +++++++++++++-
>>>  1 file changed, 13 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/Documentation/devicetree/bindings/display/msm/dp-controller.yaml b/Documentation/devicetree/bindings/display/msm/dp-controller.yaml
>>> index aed3bafa67e3c24d2a876acd29660378b367603a..0f814aa6f51406fdbdd7386027f88dfbacb24392 100644
>>> --- a/Documentation/devicetree/bindings/display/msm/dp-controller.yaml
>>> +++ b/Documentation/devicetree/bindings/display/msm/dp-controller.yaml
>>> @@ -31,13 +31,25 @@ properties:
>>>            - qcom,sm8650-dp
>>>        - items:
>>>            - enum:
>>> -              - qcom,sar2130p-dp
>>>                - qcom,sm6350-dp
>>> +          - const: qcom,sc7180-dp
>>> +
>>> +      # deprecated entry for compatibility with old DT
>>> +      - items:
>>> +          - enum:
>>> +              - qcom,sm6350-dp
>>> +          - const: qcom,sm8350-dp
>>> +        deprecated: true
>>
>> If it is only about bindings then there is little benefit in keeping
>> this, just drop this case.  However you cannot drop it from DTS, so this
>> is a bit pointless.
> 
> Our plan is:
> - land updated DT bindings, describing MST clocks on MST-enabled
>   platforms,
> - land updated DTS, adding MST clocks where applicable,

This part breaks all out-of-tree users of DTS.

> - land driver changes, keeping legacy support for non-MST DTs on
>   MST-enabled SoCs
> 
>>
>> Lack of MST support is not informative enough to claim it is not
>> compatible with 8350. For example if it was working fine via fallback,
>> then that statement is simply not correct.
>>
>> And it HAD to work fine, because there is nothing binding to
>> qcom,sm6350-dp.
> 
> It is working fine since currently we don't have MST support on the
> driver side (nor do we describe MST clocks in DT). It's true that the
> driver will have to handle non-MST DT for SM8350. However I definitely
> don't want to describe both cases in the bindings. SM6350 is not going
> to be compatible with the MST-enabled SM8350 schema.

The question is rather: is SM6350 going to be compatible (working) with
MST-enabled drivers.

Best regards,
Krzysztof